The present invention relates to an atmospheric pressure detecting method which detects atmospheric pressure as one of control conditions which is used when controlling an internal combustion engine, and an atmospheric pressure detecting apparatus used for carrying out the method.
It is sometimes necessary to use atmospheric pressure as a control condition when controlling an internal combustion engine. For example, when controlling a fuel injection quantity from an injector for supplying fuel to an engine, atmospheric pressure, intake air temperature, temperature of cooling water of the engine (temperature of the engine) and the like, other than an intake air quantity that is taken into a cylinder through an intake pipe, are detected as control conditions, and the fuel injection quantity necessary to keep an air-fuel ratio within a proper range with respect to these control conditions is determined. Therefore, in the internal combustion engine supplied with fuel from the injector, a throttle sensor for detecting an opening degree of a throttle, an intake pressure sensor for detecting intake pipe pressure at a downstream side from a throttle valve, an intake air temperature sensor, a cooling water temperature sensor and the like, as well as an atmospheric pressure sensor, are provided, so that the fuel injection quantity is arithmetically operated from output of these sensors.
As described above, it becomes necessary to mount various kinds of sensors on the engine when the fuel injection quantity from the injector is controlled. Of all these sensors, the atmospheric pressure sensor and the throttle sensor are especially expensive, and therefore it is desirable not to use these sensors in view of reducing the cost.
Thus, a speed density method is widely used as a method for controlling the fuel injection quantity from the injector. In this method, without detecting an opening degree of a throttle valve, an intake air quantity of an engine is estimated from intake pipe pressure detected at a downstream side from a throttle valve of the internal combustion engine and an engine rotational speed, and a fuel injection quantity necessary to obtain a predetermined air-fuel ratio is determined from the intake air quantity and the other control conditions. According to this method, an expensive throttle-opening sensor can be omitted, and therefore the cost can be reduced.
Meanwhile, as a method of detecting atmospheric pressure without using an atmospheric pressure sensor, the methods as disclosed in Japanese Patent Application Laid-Open Publication No. 59-188530, Japanese Patent No. 2505529, or Japanese Patent No. 2505530 are proposed.
In the method disclosed in Japanese Patent Application Laid-open Publication No. 59-188530, the intake pipe pressure at a downstream side from a throttle valve is detected as absolute pressure, and when an opening degree of the throttle valve is a predetermined value or more, and also when a rotational speed of the engine is a predetermined value or less, a correction value determined according to the throttle valve opening degree and the rotational speed of the engine is added to the intake pipe pressure, whereby an atmospheric pressure is obtained.
In the methods disclosed in Japanese Patent No. 2505529 and Japanese Patent No. 2505530, when an opening degree of a throttle valve is larger than a throttle-opening degree value previously set in accordance with a rotational speed of the engine, an atmospheric pressure is obtained by adding a correction value to the output of an intake pressure sensor which detects the intake pipe pressure.
According to the above-described conventional atmospheric pressure detecting method, the expensive atmospheric sensor can be omitted, but in the conventional atmospheric detecting method, it is essential to detect the opening degree of the throttle valve, and thus it is necessary to provide a throttle sensor in the engine. Consequently, the conventional atmospheric pressure detecting method has a disadvantage that it cannot be applied to an internal combustion engine for controlling fuel injection by the speed density method which determines the fuel injection quantity by estimating the intake air quantity from the rotational speed of the engine and the intake pipe pressure without using a throttle sensor.
Consequently, an object of the present invention is to provide an atmospheric pressure detecting method for controlling an internal combustion engine, which detects atmospheric pressure without using an atmospheric sensor and a throttle sensor, and an atmospheric pressure detecting apparatus for carrying out the method.
The present invention is applied to a method for detecting atmospheric pressure which is used as a control condition when controlling a fuel injection quantity from an injector for supplying fuel to a single cylinder internal combustion engine or a multi-cylinder internal combustion engine having an intake pipe and a throttle valve for each cylinder. In the present invention, intake pipe pressure detection means for sampling the intake pipe pressure at a downstream side from the throttle valve of the internal combustion engine at predetermined sampling intervals and detecting the sampled pressure as absolute pressure, is provided, an absolute value of a difference between a maximum value and a minimum value of the intake pipe pressure sampled while the internal combustion engine performs one combustion cycle is obtained as an intake pipe pressure change quantity, and the maximum value of the intake pipe pressure is taken as a detection value of atmospheric pressure when the intake pipe pressure change quantity is equal to or less than the set value.
In a single cylinder internal combustion engine and a multi-cylinder internal combustion engine provided with an intake pipe and a throttle valve for each cylinder, the intake pipe pressure is varied with the change of the strokes. The intake pipe pressure of the single cylinder internal combustion engine and the multi-cylinder internal combustion engine provided with the intake pipe and the throttle valve for each cylinder is reduced when an intake stroke is started, and is kept reducing until an end of the intake stroke. When the intake stroke is finished, air flows into the intake pipe due to a pressure difference between the atmospheric pressure at an upstream side from the throttle valve and negative pressure in the intake pipe, and therefore the intake pipe pressure rises to the atmospheric pressure. Seeing a change in the intake pipe pressure while the engine performs one combustion cycle, the intake pipe pressure shows the minimum value in the vicinity of timing in which the intake stroke is finished, and shows the maximum value at suitable timing during the time until the next intake stroke is started.
In a state in which the throttle valve is hardly opened, the change amount (reduction amount) of the intake pipe pressure is large, and since the next intake stroke is started before the intake pipe pressure reaches atmospheric pressure after the intake stroke is finished, the maximum value of the intake pipe pressure shows a value lower than the atmospheric pressure. On the other hand, in a state in which the throttle valve is opened to some extent or more (in a state in which a load larger than a light load is applied to the engine), the change quantity of the intake pipe pressure becomes small, and since the intake pipe pressure reaches the atmospheric pressure by the time when the next intake stroke is started after the intake stroke is finished, the maximum value of the intake pipe pressure becomes substantially equal to the atmospheric pressure. Accordingly, the absolute value of the difference between the maximum value and the minimum value of the intake pipe pressure is obtained as the intake pipe pressure change quantity, and the maximum value of the intake pipe pressure is taken as the detection value when the intake pipe pressure change quantity is equal to or less than the set value, whereby the atmospheric pressure can be detected without using an expensive atmospheric sensor and a throttle sensor.
It is preferable that the atmospheric pressure detecting apparatus for carrying out the above-described detecting method has the construction including intake pipe pressure detection means for sampling output of an intake pressure sensor, which is provided to detect intake pipe pressure at a downstream side from the throttle valve in the intake pipe provided for one cylinder of the internal combustion engine, at predetermined sampling intervals and detecting the intake pipe pressure as absolute pressure, maximum/minimum value detection means for detecting a maximum value and a minimum value of the intake pipe pressure detected while the internal combustion engine performs one combustion cycle, intake pipe pressure change quantity detection means for obtaining an absolute value of a difference between the maximum value and the minimum value detected by the maximum/minimum value detection means as an intake pipe pressure change quantity, atmospheric pressure detection condition determining means for comparing the obtained intake pressure change quantity with a previously determined set value each time the intake pipe pressure change quantity detection means obtains the intake pipe pressure change quantity and determining that the atmospheric pressure detection condition is satisfied when the intake pipe pressure change quantity is equal to or less than the set value, and atmospheric pressure detection value determining means for determining the maximum value of the intake pipe pressure detected in the maximum/minimum value detection process as a detection value of atmospheric pressure when it is determined by the atmospheric pressure detection condition determining means that the atmospheric detection condition is satisfied in all combustion cycles while the internal combustion engine performs n cycle or n cycles of combustion (n represents an integer of 1 or more).
In a state in which the rotational speed of the engine is not so high, and the amount of air flowing through the inside of the intake pipe is not large, atmospheric pressure can be detected with substantially no error by the above-described method.
However, if the rotational speed of the engine becomes high and the amount of air flowing through the inside of the intake pipe becomes large, a pressure loss in the intake passage increases, thus causing a state in which the maximum value of the intake pipe pressure does not reach the atmospheric pressure. In such a state, if the maximum value of the intake pipe pressure is taken as the detection value of the atmospheric pressure, the detection error increases. Accordingly, when the above-described detection method is carried out, it is preferable that the atmospheric pressure is detected in an operation area in which the rotational speed of the engine is equal to or less than the set value, then the detection value is stored, and with the stored detection value of the atmospheric pressure being taken as one of the control conditions, the control of the engine (for example, the control of fuel injection quantity) from a low speed area to a high speed area is performed.
When the atmospheric pressure is always needed to be detected with high precision irrespective of the rotational speed of the internal combustion engine, it is preferable that the maximum value of the intake pipe pressure detected when the intake pipe pressure change quantity is equal to or less than the set value is taken as the basic detection value of the atmospheric pressure, and the value obtained by correcting the basic detection value by the correction amount determined according to the rotational speed is taken as the detection value of the atmospheric pressure.
In this case, the correction of the basic detection value may be made by adding the correction value determined according to the rotational speed of the engine to the basic detection value, or it may be made by multiplying a correction coefficient determined according to the rotational speed of the engine by the basic detection value.
As described above, in the case of carrying out the method for obtaining the detection value of the atmospheric pressure by correcting the basic detection value which is the maximum value of the intake pipe pressure when the intake pipe pressure change quantity is equal to or less than the set value being taken as the basic detection value of the atmospheric pressure, it is preferable that the atmospheric pressure detecting apparatus for carrying out the method has the construction including intake pipe pressure detection means for sampling output of an intake pressure sensor which is provided to detect intake pipe pressure at a downstream side from the throttle valve in the intake pipe provided for one cylinder of the internal combustion engine, at predetermined sampling intervals and detecting the intake pipe pressure as absolute pressure, maximum/minimum value detection means for detecting a maximum value and a minimum value of the intake pipe pressure detected while the internal combustion engine performs one combustion cycle, intake pipe pressure change quantity detection means for obtaining an absolute value of a difference between the maximum value and the minimum value detected by the maximum/minimum value detection means as an intake pipe pressure change quantity, the atmospheric pressure detection condition determining means for comparing an obtained intake pressure change quantity with a previously determined set value each time the intake pipe pressure change quantity detection means obtains the intake pipe pressure change quantity and determining that the atmospheric pressure detection condition is satisfied when the intake pipe pressure change quantity is equal to or less than the set value, the atmospheric pressure basic detection value determining means for determining the maximum value of the intake pipe pressure detected in the maximum/minimum value detection process as a basic detection value of the atmospheric pressure when it is determined by the atmospheric pressure detection condition determining means that the atmospheric detection condition is satisfied in all the combustion cycles while the internal combustion engine performs n cycle or n cycles of combustion (n represents an integer of 1 or more), rotational speed detection means for detecting rotational speed of the internal combustion engine, map storage means storing a rotational speed/correction value map which gives relationship between the rotational speed of the internal combustion engine and a correction value which needs to be added to the basic detection value to obtain the atmospheric pressure, correction value operation means for arithmetically operating a correction value from the rotational speed/correction value map in accordance with the rotational speed of the internal combustion engine detected by the rotational speed detection means, and atmospheric pressure detection value operation means for obtaining the detection value of the atmospheric pressure by adding the correction value to the basic detection value.